1. Field of the Invention
The present invention relates to a technique for controlling communication within a network.
2. Description of the Related Art
A scheme that wirelessly connects devices located at very close range (such as 10 or so meters) to one another is called a WPAN, and is defined separately from WLAN.
At present, ECMA International, a standardization association, provides the Standard ECMA-368, which specifies physical layer and MAC layer specifications as a standard for WPAN using a UWB (Ultra Wide-Band) communication system. The Standard ECMA-368 furthermore specifies standards such as the Wireless USB standard as the protocol operating on the upper layer.
In the UWB communication scheme, the timing at which each wireless terminal accesses another wireless terminal is controlled in order to prevent wireless frame “collisions”, which occur when multiple wireless terminals transmit wireless frames simultaneously. The Media Access Control (MAC) protocol is the protocol that determines this control scheme, and implements this control through the transmission and reception of beacons.
“Interference” between wireless communication systems caused by shared frequencies presents a problem when the UWB communication scheme is used.
Reducing the transmission power of wireless terminals within the respective wireless communication systems is useful as a way to suppress the occurrence of “interference” between wireless communication systems.
In addition, various schemes for controlling the transmission power in wireless communication systems in order to conserve energy have been conventionally proposed.
For example, Japanese Patent Laid-Open No. 2005-328231 proposes a scheme in which the transmission power of a wireless terminal is progressively increased, and the transmission power level at the point in time when a link established signal has been received from an access point is set as the level to be used in subsequent data communication.
Furthermore, Japanese Patent Laid-Open No. 2002-271263 proposes a scheme in which a control station notifies a terminal station of an estimated lower limit reception power value at which the control station itself is capable of reception, and the terminal station sets its own transmission power using the estimated lower limit value as a reference.
However, both of the stated patent documents aim to control transmission power through the identification of the transmission power level necessary to maintain communication between the original terminal itself and the other wireless terminals within the wireless communication system. In other words, the stated patent documents do not aim to actively avoid “interference” with other wireless communication systems, and thus the avoidance of “interference” with other wireless communication systems cannot be guaranteed when carrying out communication using controlled transmission power.